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dbmsconcepts.html
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<!DOCTYPE HTML>
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<title>Teddy Nzioka - DBMS Concepts</title>
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<h1 id="colorlib-logo"><a href="https://teddbot.github.io">Teddy Nzioka</a></h1>
<p><strong>DBMS Concepts</strong></p>
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<h2>Most Asked DBMS Questions in Interviews</h2>
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<strong><p style="color:firebrick">What are advantages of DBMS over traditional file based systems?</p></strong>
<p>Database management systems were developed to handle the following difficulties of typical Fille-processing systems supported by conventional operating systems.<br>
1. Data redundancy and inconsistency<br>
2. Difficulty in accessing data<br>
3. Data isolation – multiple files and formats<br>
4. Integrity problems<br>
5. Atomicity of updates<br>
6. Concurrent access by multiple users<br>
7. Security problems</p>
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<strong><p style="color:firebrick">What are super, primary, candidate and foreign keys?</p></strong>
<p>A superkey is a set of attributes of a relation schema upon which all attributes of the schema are functionally dependent. No two rows can have the same value of super key attributes.
A Candidate key is minimal superkey, i.e., no proper subset of Candidate key attributes can be a superkey.<br>
A Primary Key is one of the candidate keys. One of the candidate keys is selected as most important and becomes the primary key. There cannot be more that one primary keys in a table.<br>
Foreign key is a field (or collection of fields) in one table that uniquely identifies a row of another table. See this for an example.</p>
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<strong><p style="color:firebrick">What is the difference between primary key and unique constraints?</p></strong>
<p>Primary key cannot have NULL value, the unique constraints can have NULL values. There is only one primary key in a table, but there can be multiple unique constrains.</p>
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<strong><p style="color:firebrick">What is database normalization?</p></strong>
<p>It is a process of analyzing the given relation schemas based on their functional dependencies and primary keys to achieve the following desirable properties:<br>
1) Minimizing Redundancy<br>
2) Minimizing the Insertion, Deletion, And Update Anomalies<br>
Relation schemas that do not meet the properties are decomposed into smaller relation schemas that could meet desirable properties.</p>
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<strong><p style="color:firebrick">What is SQL?</p></strong>
<p>SQL is Structured Query Language designed for inserting and modifying in a relational database system.</p>
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<strong><p style="color:firebrick">What are the differences between DDL, DML and DCL in SQL?</p></strong>
<p>Following are some details of three.<br>
<strong>DDL</strong> stands for Data Definition Language. SQL queries like CREATE, ALTER, DROP and RENAME come under this.
<strong>DML</strong> stands for Data Manipulation Language. SQL queries like SELECT, INSERT and UPDATE come under this.
<strong>DCL</strong> stands for Data Control Language. SQL queries like GRANT and REVOKE come under this.</p>
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<strong><p style="color:firebrick">What is the difference between having and where clause?</p></strong><p>HAVING is used to specify a condition for a group or an aggregate function used in select statement. The WHERE clause selects before grouping. The HAVING clause selects rows after grouping. Unlike HAVING clause, the WHERE clause cannot contain aggregate functions.</p>
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<strong><p style="color:firebrick">What is a Trigger?</p></strong>
<p>A Trigger is a code that associated with insert, update or delete operations. The code is executed automatically whenever the associated query is executed on a table. Triggers can be useful to maintain integrity in database.</p>
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<strong><p style="color:firebrick">What is a stored procedure?</p></strong>
<p>A stored procedure is like a function that contains a set of operations compiled together. It contains a set of operations that are commonly used in an application to do some common database tasks.
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<strong><p style="color:firebrick">What is the difference between Trigger and Stored Procedure?</p></strong>
<p>Unlike Stored Procedures, Triggers cannot be called directly. They can only be associated with queries.</p>
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<strong><p style="color:firebrick">What is a transaction? What are ACID properties?</p></strong>
<p>A Database Transaction is a set of database operations that must be treated as whole, means either all operations are executed or none of them.<br>
An example can be bank transaction from one account to another account. Either both debit and credit operations must be executed or none of them.<br>
ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably.</p>
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<strong><p style="color:firebrick">What are indexes?</p></strong>
<p>A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and the use of more storage space to maintain the extra copy of data.<br>
Data can be stored only in one order on disk. To support faster access according to different values, faster search like binary search for different values is desired, For this purpose, indexes are created on tables. These indexes need extra space on disk, but they allow faster search according to different frequently searched values.</p>
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<strong><p style="color:firebrick">What are clustered and non-clustered Indexes?</p></strong>
<p>Clustered indexes is the index according to which data is physically stored on disk. Therefore, only one clustered index can be created on a given database table.<br>
Non-clustered indexes don’t define physical ordering of data, but logical ordering. </p>
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